1. Field of Invention
The present invention relates to an apparatus for controlling electrically the driving system in a crawler-type tractor of bulldozers or the like.
2. Prior Art
The conventional tractor, as shown in FIG. 1, is provided with both a right-turning steering lever 2R and a left-turning steering lever 2L near the operator's seat 1, these levers 2R and 2L being linked to respective steering valves controlling a right steering clutch and a left steering clutch (not shown in the figure). Accordingly the tractor can be turned to a desired direction by selecting and operating either of the above levers 2R and 2L.
The tractor is further provided near the above steering levers 2R and 2L with a transmission lever 3, which is linked to a speed-stage selecting valve of the transmission not shown in the figure so that the transmission speed stages can be selected by operating the transmission lever 3 in accordance with the shift pattern as illustrated in FIG. 2.
In FIG. 1, reference numerals 4, 5 and 6 designate a lever for controlling a blade (bulldozer blade) not shown in the figure, a brake pedal, and an accelerator pedal, respectively.
In the driving of this conventional tractor, selecting and operating the two steering levers 2R and 2L according to the turning direction of the tractor is troublesome for the operator. Accordingly it is desirable that turning to the right or left direction can be done by operating only one lever. However, if this one lever is linked to each of the right and left steering valves, the lever is subjected to very heavy loads so that it will be difficult to perform such an operation quickly and exactly. Thus, under such circumstances, the separate right and left steering levers 2R and 2L as described above are inevitably used.
In a conventional tractor, its forward or backward movement is selected by the transmission lever 3. Therefore, when, for example, the tractor moving forward is to be driven in backward and its steering direction is to be changed, at least two levers including the transmission lever 3 must be operated. This has increased the effort on the operator.